<?php 


// var_dump($_GET);


// var_dump($_POST);


// var_dump($_REQUEST);

// $a = "hello";

// $$a = "world";

// echo $hello;

var_dump(isset($num));


// echo "https://www.baidu.com/s?";

 ?>

 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
 <html lang="en">
 <head>
 	<meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
 	<title>Document</title>
 </head>
 <body>
 	<form action="./post.php" method="get">
 		<input type="text" name="username">
 		<input type="password" name="password">
 		<input type="submit" value="注册">
 	</form>
 </body>
 </html>